The subject matter disclosed herein relates to wide bandgap semiconductor devices, such as silicon carbide (SiC) power devices, including field transistors (e.g., MOSFET, DMOSFET, UMOSFET, VMOSFET, trench MOSFET, etc.), insulated gate bipolar transistors (IGBT), and insulated base MOS-controlled thyristors (IBMCT).
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Semiconductor power devices are widely used throughout modern electrical systems to convert electrical power from one form to another form for consumption by a load. Many semiconductor power devices utilize various semiconductor devices and components, such as thyristors, diodes, and various types of transistors (e.g., metal-oxide-semiconductor field-effect transistor (MOSFETs), insulated gate bipolar transistors (IGBTs), and other suitable transistors) to perform their intended functions. Specifically for high-frequency, high-voltage, and/or high-current applications, wide bandgap semiconductor power devices can provide a number of advantages over other semiconductor device in terms of high temperature operation, reduced conduction and switching losses, and smaller die size.
Some wide bandgap semiconductor power devices may include a sputtered or evaporated metal gate electrode. However, since metals have a tendency to migrate at high temperature, a metal gate electrode can reduce the temperature capability and the reliability of a wide bandgap semiconductor power device. As such, some wide bandgap semiconductor power devices include polycrystalline silicon (polysilicon) gate electrode. Since the gate electrode should have a relatively high conductivity, such polysilicon gate electrodes are typically doped after formation of the gate electrode, for example, via treatment with phosphoryl chloride (POCl3). However, this treatment can introduce instability into the wide bandgap semiconductor power device. For example, phosphoryl chloride treatment generally results in an accumulation of dopant atoms at the surfaces of the gate electrode, including the lower surface of the gate electrode, near the underlying gate dielectric. Additionally, this treatment can result in a portion of the phosphorus dopant atoms diffusing into the gate dielectric itself. Dopant diffusion into and around the gate dielectric can negatively affect gate to source bias leakage and time-dependent gate oxide breakdown (TDDB), which are important to the performance and the reliability of the wide bandgap semiconductor power device. Additionally, thermal annealing a device after formation of the gate dielectric can result in bulk trap sites in the gate dielectric, which can cause undesirable threshold voltage shifts during device operation.